Multidose devices, both pMDIs and DPIs, show a tail-off phenomenon in the dose delivered when nearly empty; it therefore appears advisable in patients in whom the dose is critical to advise against the use of these devices past the number of recommended doses, even when the pMDI appears to be producing an adequate plume . For the Turbu-haler (Astra Pharma Inc), a dry powder device, patients need to be instructed to start a new inhaler upon appearance of the red tag in the dosing window; patients may be misled by shaking the inhaler and feeling the movement of the desiccant.
The principal difficulty experienced by patients using pMDIs is in coordinating the timing of inspiration with actuation of the device. This problem can be overcome by connecting the pMDI to a spacer . These add-on devices allow the aerosolized medication, especially the smaller particles most likely to be delivered successfully to the lower airway, to remain suspended for one or two seconds, thus providing the patient with sufficient time to initiate a deep inspiration . For patients unable to hold their breath for at least 5 s, a one-way valve at the proximal end of the spacer allows the patient to obtain an adequate dose by three or four tidal breaths in adults and five or six normal breaths in young children . For patients who are unable to produce a tight seal around the mouthpiece of the spacer, that is most children under the age six years, as well as some subjects with facial paralysis, there are spacer devices with face masks of different sizes .